Electronically controlled port fuel injection is known. An electronic controller typically issues a commanded injection time and a commanded injection duration in the form of a timed fuel pulse to individual fuel injectors each of which is dedicated to an individual cylinder of the engine. In conventional sequential port fuel injection, each injector has a dedicated injector driver controlled by the electronic controller, and the commanded injection time and duration may be tailored to the individual needs of each of the cylinders.
In conventional alternating simultaneous double fire injection ASDF, a single fuel pulse command is issued to pairs of injectors simultaneously. In some such ASDF applications, a single injector driver electrically drives a pair of injectors and thus provides for fueling of two cylinders of the engine. Other known ASDF applications may not provide for such injector driver sharing, but may require two fuel commands to be issued simultaneously, such as in a fallback mode of fuel control wherein sequential port fuel injection is at least temporarily not available.
For a given ASDF cylinder pair, ASDF control may make only one determination of the fuel requirement for the pair in each engine cycle. Then two fuel pulse commands are issued to the pair per engine cycle in most engine operating ranges. Half of the determined fuel requirement is injected at the first injection time and the other half at the second injection time. In steady state operation wherein the demand for fuel in the engine is substantially constant, there is substantially no fuel delivery error with such conventional ASDF control. However, ASDF control can introduce significant fuel delivery error during transient maneuvers, in which the engine operating point may change rapidly without proper fuel command compensation.
For example, a commanded pulse width may be calculated just before the first of two fuel commands is to be issued to the pair of cylinders in the ASDF application. The first command properly issues half of this pulse width to the pair of injectors, but by the time the second command of the engine cycle is to be issued, the needs of the engine may have changed to the extent that the uncompensated second pulse does not adequately fuel the pair of cylinders. In a transient maneuver in which the engine speed is increasing, the cylinder will be under-fueled in this case, and in a maneuver in which the engine speed is decreasing, the cylinder will be over-fueled. Such errors in fueling can degrade engine performance and increase levels of undesirable engine exhaust gas constituents.
To eliminate such errors, analysis of the fuel requirement at each of the first and second injection times has been attempted. For example, at the time of the first injection, the total fuel requirement for the complete engine cycle is applied. Then at the time of the second injection, the fuel requirement is again determined, and the difference between that requirement and the amount of fuel already injected becomes the commanded fuel pulse width for the second injection.
While this approach may substantially eliminate fuel delivery error over an engine cycle, it decreases the stability of the fuel control, leading to fueling oscillations wherein pulse width magnitude can significantly vary from the first injection to the second within a single engine cycle. This can degrade the precision of the air/fuel control in the engine, degrading performance and increasing undesirable engine emissions. Furthermore, analysis of this error reduction approach indicates it is significantly sensitive to noise in the system, wherein unmodelled inputs to the system can lead to fueling instability and significant fuel delivery error.
To further improve engine ASDF fueling accuracy during transient maneuvers, it has been proposed to determine an enrichment factor in the form of a change in commanded fuel pulse width once per engine cycle, and apply the factor to all cylinders simultaneously. The changing fueling requirements of the engine may not be provided for in such approaches, for example when the requirement changes significantly in an engine cycle.
Accordingly, what is needed is a method and apparatus for precise and stable fueling of an engine especially during transient maneuvers, and especially in ASDF port fuel injection applications.